Soft contact lenses have alleviated some of the problems that patients have experienced in not being able to wear hard contact lenses (e.g., RGP lenses) or in not being able to wear them for sufficiently long periods of time, because of initial discomfort (i.e., immediately after lens insertion), relatively long period of adapting time (a week or two) required for a patient to become accustomed to them, and/or improper fit (lenses become dislodged and/or are very uncomfortable).
Although soft contact lenses can improve wearing comfort, there may be some cornea health issues caused by wearing soft contact lenses. Unlike other tissues which receive oxygen from the blood supply, a cornea can only receive oxygen from the surrounding air. But, because soft contact lenses can conform closely to the shape of the eye, oxygen cannot easily circumvent the lens. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. Soft contact lenses must allow oxygen from the surrounding air (i.e., oxygen) to reach the cornea.
Silicone hydrogel (SiHy) contact lenses have been developed recently to allow sufficient oxygen to permeate through the lens to the cornea and to have minimal adverse effects on corneal health. SiHy contact lenses are made of a hydrated, crosslinked polymeric material that contains silicone and a certain amount of water within the lens polymer matrix at equilibrium. Water in a SiHy contact lens provides the desirable softness that enables the SiHy lens to be worn for sufficiently long periods of time and provides patients with the benefits including adequate initial comfort (i.e., immediately after lens insertion), relatively short period of adapting time required for a patient to become accustomed to them, and/or proper fit. Incorporation of silicone in a SiHy contact lens material may provide the contact lens relatively-high oxygen permeability needed for a healthy cornea.
In recent years, a great number of efforts have been made to develop contact lenses with improved wearing confort. One example is to incorporate leacheable wetting agents in contact lenses (see, e.g., U.S. Pat. Nos. 4,045,547, 4,042,552, 5,198,477, 5,219,965, 6,367,929 and 6,822,016, 7,279,507 and U.S. patent application publication Nos. 2006/0079598A1 and 2006/0251696A1, herein incorporated by reference in their entireties). Another example is to incorporate bioactive agents and hydrophobic comfort agents into contact lenses (see, e.g., U.S. patent application publication No. 2008/0124376A1 and US 2010/A1, herein incorporated by reference in their entireties).
Therefore, there is still a need for SiHy contact lenses with improved wearing confort.